Means for controlling crystal structure of materials



Jan. 1961 K. H. STEIGERWALD 2,968,723

MEANS FOR CONTROLLING CRYSTAL STRUCTURE OF MATERIALS Filed April 11,1957 3 Sheets-Sheet 1 IN V EN TOR. Aflle l/E/IVZ 577576694 1 5 W 4rrole/ ikr Jan. 17, 1961 K. H. STEIGERWALD 2,968,723

MEANS FOR CONTROLLING CRYSTAL STRUCTURE OF MATERIALS Filed April 11,1957 3 Sheets-Sheet 2 3 4 IN V EN TOR. A 1 W W W 1951 K. H. STEIGERWALD2,968,723

MEANS FOR CONTROLLING CRYSTAL STRUCTURE OF MATERIALS Filed April 11',1957' s Sheets-Sheet a INVENTOR. J mm fli/A/Z s/wmw Arr ae/rw UnitedStates Patent '9 MEANS FOR CONTROLLING CRYSTAL STRUCTURE OF MATERIALSFiled Apr. 11, 1957, Ser. No. 652,239 10 Claims. (Cl. 250-495) Germany,assignor Wurttemberg, Germany, a

This application is a continuation in part of my copending applicationSerial No. 258,673, filed November 28, 1951 now US. Patent No. 2,793,282and is specifically directed to the use of a beam of charged particlesas a heat source for controlling the crystalline structure of materials.

The use of a beam of charged particles, such as electrons, as a heatsource has been set forth in my cpending application Serial No. 640,828filed February 18, 1957 entitled Electron Beam Means for InitiatingChemical Reactions while my above noted co-pending application SerialNo. 258,673 shows the use of a beam of charged particles for producingsmall spherically shaped objects. That is, the material which is to beshaped into a sphere is exposed to an electron beam at the focus pointof the electron beam. The kinetic energy of the electrons is transferredto the material which then becomes quickly heated to its melting pointand forms a molten globule. The surface tension of the molten globuledraws it into a spherical shape and it is thereafter cooled whilemaintaining this spherical shape.

It is further possible as set forth in the above noted applicationSerial No. 258,673 to suddenly increase the intensity of the electronbeam to such a point that the object upon which the electron beam isfocused will explode and form a number of smaller objects of the desiredspherical shape.

The primary object of the instant invention is to direct chargedparticles at a material so that the crystalline structure of thematerial is controllably altered.

The material being worked may or may not be positioned at the focusedpoint of a beam of charged particles, such as electrons, which act as aflexible means for producing localized heat in the material. Forexample, in the treatment of specific areas, it is possible to increaseor decrease or vary the electron density so as to localize thermaloperations in a manner not possible heretofore.

One particular advantage lying in the use of a focused beam of chargedparticles is that small discrete areas of the material to be worked aresubjected to rapid temperature changes due to the kinetic energy of thefocused electron beam with substantially no effect on areas of thematerial adjacent to the cross-sectional area of the electron beamimpinging upon the material. By not heating the surrounding portions ofthe material as Well as not heating the containers holding the material,no impurities are produced during recrystallization of the area of thematerial which has been heated. This feature is of great importance inthe manufacture of semi-conductor devices such as germanium and silicondiodes and transistors.

My novel system has further application in the surface hardening ofmaterials wherein only an extremely thin surface layer of a material maybe re-crystallized to a more desirable crystalline structure. Thus theelectron beam and work piece may be moved relative to one another sothat the area upon which the electron beam is focused at any instant israpidly heated to a predetermined temperature whereupon the beam movesto an adjacent area and the previously heated area is quickly cooled. Byscanning the entire surface of the material, it is clear that byadequate control of the electron beam intensity and scanning time, asurface layer of predetermined thickness may be altered in any desiredmanner.

If desired, this re-crystallization process may take place in a gaseousatmosphere with the utilization of the structures set forth in myco-pending application Serial No. 640,828, which gaseous atmospherecould be at any re quired pressure and of a nature which does notchemically combine with the heated material. Conversely, the chemicalatmosphere could be of the type which would chemically combine with thesurface layer to be formed so as to olfer some desired physicalcharacteristic to the re-crystallized surface.

Accordingly, a primary object of my invention is to provide a novelmethod for controlling the crystalline structure of a material.

Another object of my invention is to utilize charged particles as a heatsource for heating discrete areas of a material to cause a change in thecrystalline structure of the heated areas.

Another object of my invention is to provide a novel system for surfacehardening a thin surface layer of a material which utilizes a focusedelectron beam as a heat source.

As has been above mentioned, my novel system for controlling the crystalstructure of materials has important applications in the field ofsemi-conductor devices. This is because my novel system may utilize afocused heat source which can raise the temperature of a smallwell-defined area of a material within a very short time and portions ofthe material adjacent the area having its temperature raised will berelatively unaffected by the application of heat. Therefore, in applyingmy novel invention to a diode or transistor device ofeither germanium orsilicon material, the crystal structure of any portion of the materialmay be controllably altered Without afiecting adjacent portions of thematerial.

Hence in a semi-conductor device of the above noted type, theconductivity of any particular portion of the device may be controlledby bringing that portion to a temperature which could cause meltingthereof. The recrystallization of that portion may then take place atsuch a rate that the impurities which control the conductivity arecontrollably disbursed in view of the difference in melting temperaturesbetween the impurities and the semi-conductor material itself. That is,the concentration of impurities can be sharply controlled bycontrollably melting and re-crystallizing the material so that theimpurities will be concentrated at some desired region in thesemi-conductor material.

This is advantageous over the normal heat means presently employed Wherethe temperature gradient from the most penetrated portion of thegermanium to the exterior has only a small slope as compared to thetemperature gradient when electron beams are employed as in my novelinvention where the temperature gradient is quite steep. Because of thesmaller slope in the former case, those impurities which tend to migrateto the hotter regions will have a longer and more difiicult travel thanis true where electrons are employed for heat. In the latter case,because of the steeper temperature gradient, these particular impuritieswould tend more easily to arrive at the hotter regions. Thus there willbe at least in that portion of the crystal which has been treated, aregion of substantially greater purity and a sharp definitiveconcentration of impurities.

Another useful application of my novel crystalline control system in themanufacture of semi-conductor devices lies in the formation of a smallprotruding point emerge at any desired location of the material, whichpoint could serve to accept terminal members for allowing connection tothe semi-conductor device. This process depends upon the novel use of afocused electron beam whereupon the temperature distribution across thearea of the electron beam is higher in the central portion than it is inthe external portions of the focused area of the beam. Therefore, byfocusing the beam on a point at which it is desired to produce aprotruding tip, the material of the small discrete area is heated to themelting point at its center while portions radially displaced from thecentral portions are not heated to the melting point. The materialwithin the molten range will then form the protruding tip.

That is, as the molten material cools in the circumferential outerregions, the contraction following such cooling causes the centralportion to move outwardly in the form of a tip. This process continueson as successive inner layers are cooled and contact, causing the centerto take on a conical shape.

Accordingly, an important object of my invention is to provide a novelcrystal structure control system for controlling the properties ofsemi-conductor materials.

Another object of the present invention is the control of thedistribution of the impurities in any materials such as semi-conductors.

Another object of my invention is to utilize a focused electron beam asa heat source for controlling the crystal structures of discrete areasof semi-conductor materials.

A still further object of my invention is to provide a novel method forproducing a protruding point on the surface of a semi-conductormaterial.

As may be seen in my co-pending application Serial No. 640,828, theintensity of the focused beam of charged particles applied to anyparticular area of a material may be controlled by either controllingthe intensity of the beam of charged particles in a continuous orintermittent manner or by causing a relative motion between the chargedparticle beam focus and the material to be heated. Since the crystallinestructure of a body is in part determined by the rate of cooling, itfollows that any heat control method can be used to control crystalstructure.

When rapid cooling or quenching is required in some particularapplication, I have provided novel means whereby the material which isto have its crystalline structure controlled is first heated inaccordance with this novel invention and is thereafter immersed in aquenching fluid. This process can be made automatic with the use ofphotoelectric emitted from the heated area are impinged upon aphotoelectric cell which energizes control equipment when the radiationsindicate that a predetermined temperature has been reached. The controlequipment then either moves the material being worked into a quenchingfluid or, if desired, could bring the quenching fluid directly intocontact with the material being heated with the material retained in itsheating position.

Accordingly, another important object of my invention is to providemeans for controlling the application of a heat source comprised of afocused beam of charged particles to a material for controlling thecrystalline structure of the material.

Another object of my invention is to controllably alter the crystallinestructure of material by controlling the length of time that a focusedbeam of charged particles is impinged upon any given area of a material.

Still another object of my invention is to control the crystallinestructure of a material by means of a focused beam of charged particleswherein heat intensity control means comprising means for causingrelative motion between the focused point of the beam of chargedparticles and the material to be heated are provided.

Another object of my invention is to provide means for controlling theintensity of a beam of charged pa r means wherein radiations ticlesutilized in controlling the crystalline structure of a material.

A further object of my invention is to provide means for causing acontrolled intermittent energization of an electron beam which isutilized for controlling the crystalline structure of a materialpositioned at the focus point of an electron beam.

A still further object of my invention is to provide means for causingquenching'of a material after it is heated by a focused electron beam.

A further object of my invention is to provide photoelectric means forautomatically causing the quenching of a heated material by a quenchingfluid after the material has been brought to a predetermined temperatureby a focused beam of charged particles.

These and other objects of my invention will become apparent from thefollowing description when taken in conjunction with the drawings, inwhich:

Figure 1 shows one embodiment of my novel invention wherein thecrystalline structure of the surface of the material to be worked is soaltered with respect to the core of the material.

Figure 2 shows a second embodiment of my invention wherein means areprovided for moving the beam of charged particles with respect to thematerial to be worked and further shows automatic means for quenchingthe heated material.

Figure 3 shows the deflecting structure utilized in the embodiment ofFigure 2 for controlling the position of the charged particle beam.

Figure 4 shows an electrical connection diagram for the structure ofFigure 3. 1

Figure 5 shows an embodiment of my novel invention wherein the workmaterial is movable with respect to the beam of charged particles andfurther shows electronic control means for intermittently energizing thecharged particle beam. 7

Figure 6 shows my novel system in conjunction with a conventional typeof electron beam production system.

Figure 7 shows the temperature distribution across the cross-sectionalarea of a focused charged particle beam and therefore illustrates thetemperature distribution of a portion of the surface of a work piecewhich is heated in the focus of the charged particle beam.

Figure 8 shows a semi-conductor crystal having a point produced thereondue to the temperature distribution set forth in Figure 7.

Referring now to Figure l which shows one manner in which a focusedelectron beam can be utilized as a heat source for controlling thecrystalline structure of a material, the electron gun system isgenerally comprised of a cathode 1, a Wehnelt cylinder 2, and an anode3. Two apertures 4 and 5 are positioned below the anode 3 and serve toreduce the scattering of the electron beam so that a narrow bundle isachieved at the output. By means of an electromagnetic lens 6, the beamof charged particles 7 may be focused on the surface of a metal cylinder-8 which is to have the crystalline structure of its surface controlledin accordance with my novel invention.

The beam producing system proper may be adjusted by means of the screws9, 10, 11 and 12 which control the alignment of the beam. The completeelectron gun system is housed in chamber 13 which is kept under a highvacuum by means of a diffusion pump 14.

The electron beam producing system described above is particularlycapable to supply a beam of electrons which are focused at a remotepoint and is completely described in my U.S. Patent No. 2,771,568 issuedNovember 20, 1956, and reference is made thereto for further detailsregarding this electron gun structure. It is to be clearly noted,however, that any electron gun structure could be utilized, the onlyimportant thing being that a beam of focused electrons is provided tooperate as a heat source. Furthermore, the use of an electron beam isset forth herein for illustrative purposes only and a asesyas beam ofpositive or negative ions could be utilized as well as a beam ofnegative electrons.

The material which is to have its surface characteristic controlled inaccordance with my novel invention is shown as the metal cylinder 8which is rotatably mounted between pivot members 16 and 17 within achamber 15. More specifically, a motor i8 is connected to rotate spindle19 which is connected to displace table 20 in a direction perpendicularto the axis of the electron beam 7.

A gear 21 is coaxially connected to spindle 19 and is positioned toengage gear 22 which is coaxially fastened to worm 23, whereby rotationof gear 22 effects rotation of the worm 23. The worm 23 then engagesgear member 24. Gear member 24 is a bevel gear and engages a cooperatingbevel gear 25 which is connected to rotate the spindle 17 which is oneof the pivotal mounting points of the work material 8.

In operation, by energizing motor 18, spindle 19 will rotate to causethe table 23 to be moved in a direction perpendicular to the axis of theelectron beam at a predetermined rate. Since the mounting members ofpivotal mounting members 16 and 17 are fastened to table 20, the workmaterial 8 will be translated in this perpendicular direction with thetable 20. Furthermore, since rotation of spindle 19 causes a rotation ofworm gear 23, through the cooperating gears 21 and 22, the bevel gear 24(which is pivotally mounted on a structural member not shown but ismovable with the table 20) drives bevel gear 25 to cause a rotation ofthe work material 8.

Accordingly, the single drive motor 18, when energized, will cause thework material 8 to thread past the focused point of electron beam 7. Byproperly coordinating the vertical displacement speed of table 20 andthe angular velocity of work material 3, the entire surface of cylinder8 may be swept past the focus point of the charged particle beam.

At any one instant, the particular area of the work material 8 which isexposed to the charged particle beam will be heated to a predeterminedtemperature. This area will thereafter be removed from the focusedcharged particle beam and will be rapidly cooled. In this manner thecrystal structure of each discrete area will be exposed to the beam andwill be heated and thereafter rapidly cooled.

By way of example, the cylinder 8 could comprise a cylinder of steelhaving a diameter of 2 cm. and a length of 5 cm. Cylinder 8 may berotated at a speed of 5 revolutions per second and the table 20 may bedisplaced at a speed of 5 mm. per second. When the cross section of thecharged particle beam at its focus point is approximately 1.1 mm., theentire surface of cylinder 3 may be exposed to the charged particle beamwithin ten seconds.

By then making the beam current intensity approximately milliampereswith an accelerating voltage of sixty thousand volts, it has been foundthat the discrete surface areas exposed to the beam of approximatelytwenty microns thickness are heated to 1200 C. during the operatingprocess. That is to say, the surface material is raised to 1200 C. onlywhen that particular area is exposed to the electron beam. The coolingof the individual heated surface elements after being taken away fromthe focused electron beam occurs so quickly that the crystallinestructure is altered in a manner that would be obtained by quenching thematerial so as to achieve an extremely hard thin surface layer.

It is important to note that during this process, the entire cylinder isheated to an average temperature of only 150 C.

Clearly, the surface thickness of the hardened layer as well as thehardness of the layer may be easily controlled by altering anycombination of accelerating voltage, beam current, and the time duringwhich a particular area is exposed to the focused electron beam, thistime being determined by the angular velocity of the work material aswell as the rate of displacement of the work table.

In many cases it may be desirable to expose cylinder 8 to the crystalstructure control beam 7 with the surface of the material exposed to agaseous atmosphere which may be at any pressure. This gaseous atmospherecould be chemically inert with respect to the material being heated or,if desired, the gas could have some chemically reducing elfect whichwould enhance the hardening of the surface work piece.

As has been set forth in my U.S. Patent No. 2,793,281, issued May 21,1957, one or more intermedIate pressure chambers may be utilized toisolate the low pressure of an electron beam producing system from thehigher pressure of the gaseous atmosphere exposed to the material to beworked while still preventing interference of the electron beam lowpressure system from the high pressure gaseous atmosphere.

This system is set forth in Figure l as comprising the intermediatepressure chamber 27 which contains apertures 28 and 29 wherein thedistance between the two openings 28 and 29 which are in registry withthe electron beam 7 and the area to be heated on the surface of thematerial 8 are kept smaller than the mean free path of the gas moleculescontained therein. The pressure within intermediate pressure chamber 27is controlled to be intermediate between the pressure within theelectron beam producing system and the work material chamber by means ofa vacuum pump 28.

The gaseous atmosphere is supplied to the work material chamber 26 froma tank 29 which is connected to the pressure chamber through a conduit30, control valve mechanism 33 and conduit 32. A conduit 34 thenconnects vacuum pump 35 to pressure chamber 26 whereby pressure and gasflow within the chamber 25 may be controlled by valve mechanism 33.

While Figure 1 shows my novel invention with the use of a singleintermediate pressure chamber, it is to be understood that any desirednumber of intermediate pressure chambers may be utilized. By way ofexample, Figure 2 which shows a second embodiment of my novel inventionutilizes a first and second intermediate pressure chamber. In Figure 2,two apertures 36 and 37 are positioned below the anode 3 to limit thescattering of the electron beam. The vacuum chamber 38 is connected to ahigh vacuum pump (not shown) through the conduit '40 and in this manneris kept at a hard vacuum.

The aperture 37 is in the center of a conically shaped extension of onewall of the high vacuum enclosure and is positioned adjacent a similarconical partition 41 which includes an aperture 42. A further partition43 which contains an opening 44 is positioned beneath partition 41.

In this manner (as is more fully described in .copending applicationSer. No. 640,828), a first and second intermediate pressure chamber 45and 46 respectively are created with their apertures in alignment withthe charged particle beam and the work material. That is to sayapertures 37, 42 and 44 will allow the electron beam access to theactual work chamber 47 which contains the material to be worked.

The intermediate pressure chamber 45 is connected to a vacuum pump (notshown) through the conduit 48 and in this manner may be kept at somedesired pressure. The intermediate pressure chamber 46 is connected to asecond vacuum pump (not shown) through the conduit 49 whereby thepressure of this intermediate chamber is kept at some predeterminedpressure.

As was the case in the single intermediate pressure chamber of Figure l,the adjacent aperture of the various intermediate pressure chambers arespaced at a distance from one another which is less than the mean freepath of the gas molecules within the intermediate pres sure chamber.

Accordingly, the material 50 which is to have its crystalline structurecontrolled by the heat of the focused electron beam may be positioned inany desired gaseous atmosphere of any desired pressure by utilizing theabove described intermediate pressure chamber system which isolates thevacuum system of the electron gun and its surrounding gaseousatmosphere.

Figure 2 also differs from Figure 1 in the-manner in which relativemotion between the electron beam and the work material surface isobtained. That is, in Figure 1 this relative motion was achieved bymaintaining the beam position steady and moving the work material.

igure 2 shows a manner in which the work material may be held rigid andrelative motion is achieved by deflecting the beam in accordance withthe beamdeflecting system set forth in my copending application Ser. No.258,672.

In Figure 2 the deflecting system which is further shown in Figures 3and 4 includes four energizing coils 51, 52, 53 and 54, respectively.

As is best seen in Figure 3, which is a top view of the magnetic controlstructure, coils 51 and 52 are wound on diametrically opposite magneticpole pieces while coils 53 and are 90 displaced from coils 51 and 52 andare wound on similar protruding magnetic pole pieces. Each of the polepieces have their inner ends terminated adjacent a non-ferro-magneticring 115 while their outer ends are terminated in ring 116 offerromagnetic material which closes the magnetic lines of flux of eachof the pole pieces.

One manner in which the control windings 51 through 54 may be connectedis set forth in Figure 4 wherein A.-C. power is connected to the primarywinding 117 of a transformer having secondary windings 118 and 119.Winding 118 is connected through a switch 120 and across a potentiometer121 while winding 119 is connected through switch 122 to potentiometer123.

A tap 124 then connects coils 53 and 54 in series with one another forcontrollable excitation from transformer winding 118 while coils 51 and52 are connected in series and are energized through transformer winding119 through tap 125.

By adjustably varying taps 124 and 125 the current flowing through thedeflecting coils 5'1 and 54 may be regulated. By way of example, if thetwo taps are so adjusted that the current flowing through coils 51 andS2 is the same as the current flowing through coils 53 and 54 and if aphase quadrature voltage is applied to the two potentiometers 121 and123, the magnetic field created by coils 51 through 54 will cause thecharged particle beam to describe a circle on the surface of materialSit of Figure 2. By adjustably controlling the excitation of coils 51through 54, it is therefore seen that any desired pattern of surfaceheating of the surface of work material 5% may be achieved to therebyachieve any predetermined hardening pattern of that surface.

When it is necessary to harden a relatively thick surface layer of amaterial such as material 5% of Figure 2 it is possible that the smallareas of the surface which have been exposed to the heating effect ofthe electron beam consecutively cannot be cooled quickly enough toobtain the required quenching by heat exchange with the remainingmaterial.

A similar problem arises in heating a volume of mate rial whichconstitutes a substantially large portion of the entire body itself. Insuch construction, it is not possible to rely on the unheated portion toconduct away the heat at the desired high rate. To allow rapidquenching, I have provided a novel means for bringing the heated objectinto a cooling medium whereby rapid quenching is achieved. Thisstructure is set forth in Figure 2 and comprises the chamber 55 which ispositioned below the work chamber 47. The work material 50 is positionedon a plate 57 which has a recess 58 therein. A first and second coil 66and 61 respectively, having movable cores 62 and 63 are coupled to theplate 57 by any desired flexible coupling means. Thus when the cores 62and 63 are in the left hand position shown in Figure 2, the solidportion of plate 57 is positioned beneath the object to be worked 50.When, however, coil is energized as will be described hereinafter, theplate 57 will be moved to the right whereby aperture 58 will be movedinto registry with work material 50 and work material 50 will dropthrough the aperture 53 and into the cooling medium within chamber 55.

Clearly, the winding 60 could be manually energized to allow quenchingof the heated surface of material Stl to proceed. However, it may bemore desirable to have the time of quenching determined by automaticmeans which would be more accurate than would a human operator.

This automatic quenching means is seen in Figure 2 and comprises thephotocell 126 which is contained Within the base plate of the deflectingsystem of coils 51 through 54. The light emanating from the heatedsurface of work piece 50 falls on this photocell to cause energizationthereof. Since the light emanating from the heated surface of workmaterial 50 is a function of the temperature of that surface, the outputvoltage of photocell 126 will also be related in some manner to thetemperature of the surface of work material 50. By connecting the outputvoltage of photocell 126 to relay 66 which could be of any well knowntype, the relay may be operated on a predetermined input voltage tocause energization of winding 60 of the electromagnet control systemwhereby core 62 will be pulled into the solenoid coil of and the workmaterial 50 will drop through aperture 58 and into the quenching fluid.Hence the heated surface of work material 50 will be quenched once thissurface reaches a predetermined temperature.

In order to reset the plate 57 to receive a new work piece a lightsource 67 and a second photocell 6 8 may be provided wherein the workmaterial 50 is interposed between these two elements so as to normallyblock the impingement of light source 67 upon photocell 68. When,however, plate 57 is moved to the left and work piece 50 is dropped,photocell 68 is energized by light from the light source 67 toreenergize relay 66 in such a manner that coil 60 is deenergized andcoil 61 is energized. With the energization of coil 61, plunger 63 willbe pulled into the solenoid coil 61 to thereby reposition platform 57for the reception of a new work piece.

One application of my novel invention which requires the use ofadditional quenching means of the type set forth in Figure 2 utilizes awork material 50 which is a steel member having a length of 10 cm., awidth of 3 cm. and a thickness of 1 cm. A beam current of intensity often milliamperes at an acceleration voltage of 100,000 volts is utilizedand the work piece is scanned for approximately ten seconds by a chargedparticle beam having a diameter of 5 mm.

For this purpose, a control voltage is applied to deflecting coils 51and 52 at a frequency of 50 cycles per second while a control voltagehaving a frenquency of 600 cycles per second is applied to deflectingcoils 53 and 54 whereby the individual traces of the charged particlebeam overlap on the surface of the steel work material so as tocompletely cover the surface. With this combination of parameters, asurface layer having a thickness of forty microns is heated to 1200 C.and it was found that in order to achieve suflicient cooling for thedesired surface hardening, it was necessary to utilize the additionalquenching of a cooling fluid as set forth in Figure 2.

While the structures of Figures 1 and 2 have utilized heat control meanswhich includes structures for causing relative motion between the beamof charged particles and the surface to be heated, it is to beunderstood that heat control could be also obtained through anintermittent energization through either a gradual control of the beamcurrent intensity or through an intermittent control of the beamcurrent.

Certain other advantages are provided by causing intermittent beamcontrol since the heating of the material does not continuously varyfrom one area to an adjacent area but is applied to a first area and isthereafter turned off and then applied to a second discrete area. Hence,the cooling of the first area is unaffected by the heating of the secondarea. Furthermore, with the use of intermittent energization of thebeam, it is easier to obtain a variable heating effect along the surfaceof the body which is to be worked. In this manner, various structuraldiiferenecs may be taken into consideration when heating a body as forexample, when heating a body having a sharp edge to which less heatshould be applied to obtain a predetermined hardening.

One manner in which the beam current could be intermittently controlledis set forth in Figure and is based on the intermittent control systemset forth in my above noted application Serial No. 640,828. Morespecifically, Figure 5 shows a beam control system which in essencecomprises a multivibrator type of control where the multivibratorincludes triodes 69 and 70 which have a common cathode resistor 71. Theplates of each of triodes 69 and 70 are connected through plateresistors 72 and 73 respectively which are terminated at terminal 76while their grids are connected through adjustable grid resistors 74 and75 which, along with common cathode resistor 71, are connected to thegrounded terminal 77.

In operation, adjustment of the grid resistor 74 will regulate thelength of time during which the electron beam is turned off and gridresistor 75 will control the length of time that the beam is turned on.The voltage input for the multivibrator system is applied acrossterminals 76 and 77 and regulation of this voltage will regulate theintensity of the electron beam impulses.

Terminal 76 is also connected to a D.-C. biasing voltage source 78 wherethe polarity of this source is indicated in the figure. This voltagebiases the grid potential of Wehnelt cylinder 79 to some predeterminedpoint while the high voltage supply is connected at terminal 80 andthrough the protective resistor 81. Terminals 82 and 83 have voltagesources applied thereacross for supplying the heater current of cathode84.

Since terminal 82 is also connected to the high voltage supply 80, thepotential of the Wehnelt cylinder 79 will be maintained at a potentialdifiierence with regard to cathode 84 which is determined by thepotential of the D.-C. bias 78. By Way of example, if the high voltagesupply at terminal 80 is minus 50,000 volts while the voltage of D.-C.bias 78 is 400 volts, the Wehnelt cylinder 79 will be normallymaintained at a potential dif ference of minus 400 volts with respect tocathode 84 which is normally sufficient to suppress the energization ofthe electron beam. When, however, plate current flows through tube 70, apositive impulse is applied to the Wehnelt cylinder 79 over conductor100 so as to unblock the electron beam and cause the initiation of abeam impulse. By controlling grid resistors 74 and 75 in an appropriatemanner the duration of time during which the tube 70 conducts may beadjustably controlled whereby the initiation of the electron beamimpulse is similarly controlled.

It is to be noted that a condenser 86 is connected between terminal 82and anode 85 which is connected to ground potential. This condensercharges during an impulse pause and is discharged during the initiationof an impulse to thereby give a clearly defined electron impulse currentas has been described in my co-pending application Ser. No. 640,828.

The remaining electron beam producing structure is similar to thathereinbefore described and includes diaphragms 86 and 87 which haveapertures therein for 10 limiting the scattering of the electron beam.The chamber 88 within which the electron gun system is housed isconnected to a vacuum pump through conduit 89 and is kept at a highvacuum.

As was the case in Figure l and as is described in my co-pendingapplication Ser. No. 640,828, the electron beam 92 may be focused by anelectromagnetic lens 90. This electromagnetic lens is designed to haveupper pole shoes 91' and lower pole shoes 92' which form an intermediatepressure chamber 93 which is kept at a predetermined pressure by vacuumpump means connected to the conduit 94.

A small hollow tube 95 is introduced into the lower pole shoes 02 as wasdescribed in my co-pending application Ser. No. 640,828 wherein thesmall aperture of tube 95 which is sufiicient only to pass the smalldiameter of the focused electron beam and offers relatively highresistance to the passage of gas molecules which attempt to flow intothe lower pressure region of lower pressure chamber 93. A furtherintermediate pressure chamber 96 is positioned below pressure chamber 93and is maintained at a predetermined temperature through the conduit 97which is attached to some suitable vacuum pump means.

A still further intermediate pressure chamber 98 is positioned belowchamber 96 and is maintained at a predetermined pressure by vacuum pumpmeans con nected to conduit 99. The material 91 which is to have thecrystalline structure of its surface controlled in accordance with theinstant invention is positioned on a table 101 which may be moved on afurther table 102 by a spindle 103 which is rotatable by means of thecrank 104. The table 102 is in turn movable with respect to the bottom105 of the work chamber 106 by means of a dove-tailed guide. It is to benoted that for allowing this type of movement that the spindle 103 maybe translated through a slotted arrangement in the left hand wall ofchamber 106. In order to move table 102 there is a similar spindle andcrank arrangement to the spindle and crank 103 and 104 respectivelywhich is not seen in the figure.

Since the direction of displacement of the two tables 101 and 102 isperpendicular to one another, it is possible to position the surface ofmaterial 91 in any desired manner with respect to the beam 92.

If it is desired to Work the surface of material 91 in the presence ofan inert gas or in the presence of a chemically active gas, the gas maybe supplied from a container 107 through a conduit 108 and into thechamber 106. Chamber 106 is also connected to an exhaust pump (notshown) through conduit 109.

In the embodiment of Figure 5 the temperature control is achieved bycausing the electron beam to be impinged upon the material to be Workedin an intermittent manner. Therefore, the material is first heated andwhen the beam is turned off there is ample time for the heat to berapidly conducted to adjacent portions of the material which were notsubjected to the electron beam, and adequate quenching of the small areawhich has been heated may result.

By Way of example, it is possible to harden the point of a phonographpick-up needle by impinging an electron beam upon the tip of the needlefor 1 10- seconds with a beam current intensity of 10 milliamperes at anaccelerating voltage of 80,000 volts.

In another application of the device in Figure 3, a germanium crystalmay be placed in the position of material 91 whereby the crystallinestructure and distribution of impurities of the crystal are controlled.

By way of example, with an impulse duration of 10- seconds, a beamintensity of 0.2 milliampere, and an accelerating voltage of 50,000volts at small area of about 50 microns in diameter may be heated to1,000 C. to a depth of approximately 10 microns.

As is well known, this control of conductivity is essential in themanufacture of semi-conductor devices such as transistors. If desired,any area of any desired configuration could be melted, as set forthabove, by appropriate control of crank 104 and the impulsing system.

Figure 6 sets forth a still further embodiment of my invention whereinheat control is obtained through a continuous control of the chargedparticle beam intensity. In Figure 6 the electron gun structure is ofthe conventional type and comprises a cathode 126, a Wehnelt cylinder127, and an anode 128. The anode high voltage supply for acceleratingthe charged particle beam is connected at terminal 134. The filament ofthe cathode 126 is heated by a voltage source (not shown) which isconnected across terminals 130 and 131. A variable voltage source 133 isthen connected in series with the Wehnelt cylinder 127, a protectiveresistor 135, and a high voltage supply 134.

Thus, the high voltage supply connected to terminal 134 can be of theorder of 50,000 volts while the voltage source 133 could be of the orderof 300 volts. Hence, the cathode 126 would be at a potential of minus50,000 volts while the Wehnelt cylinder 127 is at a potential of minus50,300 volts. Clearly, by regulating t.e voltage source 133 it ispossible to vary the intensity of the charged particle beams supplied bythe electron gun structure from some conduction value to a cut-offpoint.

The work chamber 106 of Figure 6 which could be similar to that setforth in either of Figures 2 or 5 is shown as including a table 136 inFigure 6 which supports the work material 91. In order to achieverelative motion between the electron beam or charged particle beam andthe work material 91 an electromagnetic deflecting system of the typeset forth in Figure 2 is provided.

In operation, the object 91 could be a germanium crystal which isscanned by a charged particle beam having a diameter of /2 millimeter.The beam current intensity may be A2 of a milliampere and anaccelerating voltage of 50,000 volts with the beam moving relative tothe work material at a speed of 1 centimeter per second. With this setof parameters it has been found that the scanned surface layer is heatedto approximately l,000 C. and is thereby melted as this is above themelting point of germanium. In this manner the conductivity of thesurface layer may be controlled in some defined manner.

it is to be noted that by changing the parameters above recited that anytype of material could be utilized. Thus, silicon which has a highermelting point than germanium could be worked upon in a similar manner.

It is also to be noted that a plurality of objects could be positionedin the place of the single object 01 of Figure 6 wherein each of theobjects are scanned in turn by the deflecting system.

The temperature distribution across the diameter of the focused chargedparticle beam has been found to be that set forth in Figure 7. Morespecifically, Figure 7 shows that the central portion of thecross-sectional area of the beam has a higher temperature than do theoutward portions, as is to be expected.

In radiating a germanium crystal such as the crystal 111 of Figure 8with a charged particle beam having the temperature distribution setforth in Figure 7, the intensity of the electron beam may be socontrolled that the temperature t of Figure 7 is the melting point ofthe crystal 111. Thus, by applying this beam to the crystal 111 it isseen in Figure 7 that only the region between diameters (II. and d2 isbrought to the melting point while the external portions are maintainedin their solid state. in this way any contamination of the crystal byheating of other material adjacent to the crystal is completely avoidedand possibilities of external contamination of the crystal aresubstantially reduced.

If, in the use of the embodiment of Figure 6, the beam is first appliedto a material such as germanium crystal 111 of Figure 7 so that only thecentral portions of the focused beam will cause melting in the crystaland the beam intensity is fully reduced so as to cause a controlledcooling of the molten material, a point, such as the point 113 of Figure8, has been found to grow on the crystal. This point is symmetrical andmay be advantageously used in the connection of an electrode.

Furthermore, the material of point 113 and its surrounding areas containa higher impurity concentration because of the diffusion of impuritiesto the portion which is at a higher temperature whereby, for example,the conductivity or any other property of the tip is easily controlled.

By way of example, in using the device as set forth in Figure 6, whereina charged particle beam of 0.2 millimeter in diameter and a beamintensity of 0.2 milliampere and an acceleration voltage of 50,000 voltsis impinged on the crystal for approximately 1 second, and thereafterdecreased to cut-off in approximately 10 seconds, a point is formed onthe original germanium crystal. if desired, this process may be socontrolled that after the original point is formed, a second point maybe formed on an adjacent portion so as to form any desired uplifted orembossed pattern on the crystal.

Although I have described preferred embodiments of my novel invention,many variations and modifications will now be obvious to those skilledin the art, and I prefer therefore to be limited not by the specificdisclosure herein but only by the appended claims.

I claim:

1. The method of controlling the crystalline structure of a material;said method comprising the steps of positioning the material to have itscrystalline structure controlled in a predetermined position, directinga beam of charged partcles at said material and focusing said beam ofcharged particles on a predetermined crosssectional area portion of saidmaterial as defined by the cross-sectional area of said beam of chargedparticles bringing the said predetermined portion of said material to apredetermined temperature, and thereafter controllably affecting theapplication of said focused beam of charged particles to saidpredetermined portion of said material to allow a predeterminedcontrolled decrease in the temperature of said heated predeterminedportion to control the recrystallization of said predetermined portionin a predetermined manner.

2. The method of controlling the crystalline structure of a materialcomprising the steps of focusing a beam of charged particles to act as aheat source on the surface of said material until a surface portion ofsaid material defined by the cross-sectioned area of said beam ofcharged particles impinging thereon is brought to a predeterminedtemperature and thereafter varying the relative position of said focusedbeam with respect to said material surface whereby said beam moves overa predetermined surface area of said material; the relative motionbetween said beam and said surface of said material being controlled topermit a predetermined controlled cooling of any heated discrete area ofsaid surface area when said charged particle beam is removed to anotherdiscrete area during said scanning process to produce a thin surfacehardened shell.

3. The method of controlling the crystalline structure of a material;said method comprising the focusing of a beam of charged particles toact as a heat source on a portion of said material whereby thecross-sectional area of said material defined by the cross-sectionalarea of said beam of charged particles is brought to a predeterminedtemperature and thereafter affecting the application of said focusedbeam of charged particles to said portion to allow a predeterminedcontrolled decrease in the temperature of said portion to control therecrystallization of said portion in a predetermined manner bycontrolling the intensity of said beam of charged particles in apredetermined manner.

4. The method of controlling the crystalline structure of material; saidmethod comprising the focusing of a beam of charged particles to act asa heat source on a portion of said material whereby the cross-sectionalarea of said material defined by the cross-sectional area of said beamof charged particles is brought to a predetermined temperature andthereafter affecting the application of said focused beam of chargedparticles to said defined area to allow a predetermined controlleddecrease in the temperature of said heated area to control therecrystallization of said area in a predetermined manner by controllingthe intensity of said beam of charged particles by intermittentlyenergizing and cutting off said beam of charged particles applied tosaid predetermined area.

5. The method of controlling the crystalline structure of a materialcomprising the steps of focusing a beam of charged particles to act as aheat source on the surface of a material to have its crystallinestructure controlled and retaining said focused beam of chargedparticles on a predetermined surface area of said material until saidpredetermined surface area is brought to a predetermined temperature andthereafter cooling said predetermined area in a predetermined controlledmanner to controllably afiect the crystalline structure of saidpredetermined area in a predetermined manner.

6. The method of controlling the crystalline structure of a materialcomprising the steps of focusing a beam of charged particles to act as aheat source on the surface of said material until a surface portion ofsaid material defined by the cross-sectional area of said beam ofcharged particles impinging thereon is brought to a predeterminedtemperature and thereafter moving said beam of charged particles to aposition removed from said area brought to said predeterminedtemperature to permit a controlled decrease in temperature of said areato control the recrystallization of said area.

7. The method of controlling the crystalline structure of a materialcomprising the steps of focusing a beam of charged particles to act as aheat source on the surface of said material until a surface portion ofsaid material defined by the cross-sectional area of said beam ofcharged particles impinging thereon is brought to a predeterminedtemperature and thereafter moving said material with respect to thefocal point of said focused charged particle beam to permit apredetermined decrease in the temperature of the portion of saidmaterial which was brought to said predetermined temperature to permit acontrolled recrystallization of said portion.

8. The method of controlling the crystalline structure of material; saidmethod comprising the focusing of a beam of charged particles to act asa heat source on a portion of said material whereby the cross-sectionalarea of said material defined by the cross-sectional area of said beamof charged particles is brought to a predetermined temperature andthereafter affecting the application of said focused beam of chargedparticles to said defined area to allow a predetermined controlleddecrease in the temperature of said heated area to control therecrystallization of said area in a predetermined manner by controllingthe intensity of said beam of charged particles by intermittentlyenergizing and cutting off said beam of charged particles applied tosaid predetermined area, and thereafter causing relative motion betweensaid focused beam of charged particles and said material to apply saidfocused beam at a different portion of said material.

9. The method of controlling the crystalline structure of a materialcomprising the steps of focusing a beam of charged particles to act as aheat source on the surface of a material to have its crystallinestructure controlled and retaining said focused beam of chargedparticles on a predetermined surface area of said material until saidpredetermined surface area is brought to a predetermined temperature andthereafter cooling said predetermined area in a predetermined controlledmanner to controllably affect the crystalline structure of saidpredetermined area in a predetermined manner by bringing a quenchingmedium into contact with said material.

10. The method of controlling the crystalline structure of a materialcomprising the steps of focusing a beam of charged particles to act as aheat source on the surface of a material to have its crystallinestructure controlled and retaining said focused beam of chargedparticles on a predetermined surface area of said material until saidpredetermined surface area is brought to a predetermined temperature andthereafter cooling said predetermined area in a predetermined controlledmanner to controllably affect the crystalline structure of saidpredetermined area in a predetermined manner by moving said materialinto a quenching medium when the said portion of the surface area ofsaid material reaches a predetermined temperature.

References Cited in the file of this patent UNITED STATES PATENTS2,244,056 Denneen et al June 3, 1941 2,267,714 'Borries et al Dec. 30,1941 2,267,752 Ruska et al Dec. 30, 1941 2,423,729 Ruhle July 8, 19472,771,568 Steigerwald Nov. 20, 1956 2,778,926 Schneider Jan. 22, 19572,793,282 Steigerwald May 21, 1957

